We present the Flyweight Object-Oriented (Fᴏᴏ) calculus for the modeling of object-oriented languages. Fᴏᴏ is a simple, minimal class-based calculus, modeling only essential computational aspects and emphasizing larger-scale features (e.g., inheritance and generics). Fᴏᴏ is motivated by the observation that recent language design work focuses on elements not well-captured either by traditional object calculi or by language-specific modeling efforts, such as Featherweight Java. Fᴏᴏ integrates seamlessly both nominal and structural subtyping ideas, leveraging the latter to eliminate the need for modeling object fields and constructors. Comparing to recent formalization efforts in the literature, Fᴏᴏ is more compact, yet versatile enough to be usable in multiple settings modeling Java, C#, or Scala extensions.

Java generics are compiled by-erasure: all clients reuse the same bytecode, with uses of the unknown type erased. C++ templates are compiled by-expansion: each type-instantiation of a template produces a different code definition. The two approaches offer trade-offs on multiple axes. We propose an extension of Java generics that allows by-expansion translation relative to selected type parameters only. This language design allows sophisticated users to get the best of both worlds at a fine granularity. Furthermore, our proposal is based on Java 8 Type Annotations (JSR 308) and the Checker Framework as an abstraction layer for controlling compilation without changes to the internals of a Java compiler.

We propose DelphJ: a Java-based OO language that eschews inheritance completely, in favor of a combination of class morphing and (deep) delegation. Compared to past delegation approaches, the novel aspect of our design is the ability to emulate the best aspects of inheritance while retaining maximum flexibility: using morphing, a class can select any of the methods of its delegatee and export them (if desired) or transform them (e.g., to add extra arguments or modify type signatures), yet without needing to name these methods explicitly and handle them one-by-one. Compared to past work on morphing, our approach adopts and adapts advanced delegation mechanisms, in order to add late binding capabilities and, thus, provide a full substitute of inheritance. Additionally, we explore complex semantic issues in the interaction of delegation with late binding. We present our language design both informally, with numerous examples, and formally in a core calculus.

Deadlocks can have devastating effects in systems code. We have developed a type and effect system that provably avoids them and in this paper we present a tool that uses a sound static analysis to instrument multithreaded C programs and then links these programs with a run-time system that avoids possible deadlocks. In contrast to most other purely static tools for deadlock freedom, our tool does not insist that programs adhere to a strict lock acquisition order or use lock primitives in a block-structured way, thus it is appropriate for systems code and OS applications. We also report some very promising benchmark results which show that all possible deadlocks can automatically be avoided with only a small run-time overhead. More importantly, this is done without having to modify the original source program by altering the order of resource acquisition operations or by adding annotations.